Cables: Speaker Cable Design, Part 2

Part 1 of this article in the previous issue ended with the design brief for conductors in a speaker cable. I described why I chose a star-quad geometry using a 20-mil wire diameter in a 24-wire (12 bonded pairs) woven polarity. We continue with the next subheads under the Design Brief for speaker cables.

2) Dielectric materials

Again, Teflon® was chosen as it is the best solid dielectric there is. I needed a thin wall to bring the wires close together for inductance reduction, but capacitance is an issue with 24 closely spaced wires.

A capacitor is two parallel conductive plates with an insulator between them. To lower capacitance, I wanted a low-dielectric-constant plastic (Teflon®). To achieve the required low capacitance, more needs to be done to “thicken” the insulation without increasing loop area effects. This seems impossible to do, but it isn’t with the woven design described above. The final insulation wall was driven by balancing capacitive gains with inductive reduction. Dielectric geometry allowed this balance to be accomplished.

3) Dielectric geometry

The requirement to meet capacitance also drove the design to a weave pattern. Each polarity is separate; there is no interweaving of same polarity wires. What if we had wires with several AWG sizes? Current will flow along the path of least resistance. This does not mean current won’t flow in specific wires, just that the majority of the current magnitude is shifted to the easier path. Every wire will have current at all frequencies. The magnitude will change and follow Ohm’s law. Many differing wires sizes and electrical lengths can impact the signal arrival times across the audio band based on physical conductor lengths in composite wire-size designs.

If we take two wires with the same skin depth (same frequency point being considered), but one wire has twice the surface area, more current will flow into the larger surface area wire. It offers less resistance. But, the lower resistance wire is larger, and not ideal if we want the current across the wire to be more uniform. Bigger wires are better at lowering resistance at a given frequency because they have the most surface area. We use this at RF with a “skin” of copper to carry the lowest, yet still high, frequencies efficiently. The wire’s core under the copper is a material that is “filler” and has no current flow, such as steel or aluminum.

At lower frequencies the current is diffusion coupled evenly through the entire wire. So if you send just low frequencies, use as low a DCR wire as you can get.

Those are the extremes. Audio is weird in that we need to improve current coherence through the wire while it is trying to move to the outside surface. We don’t care about attenuation as much since it is negligible at audio frequencies. We make the conscious decision to go for forced current coherence with more small wires. This technically violates the practice of more “surface” area for lower attenuation at high frequencies for current coherence. Big wire offers more surface area for lower attenuation, while small wire offers better current coherence, but higher attenuation.

With interconnects, if you use one wire, the current delivery has to be considered to the load. RCA and XLR cables have near zero current flow into the high impedance load, so we can go for signal current coherence and suffer little attenuation. Speaker cables can’t use too few wires as there are 20-30 amps coursing through a speaker cable.

Good audio performance is about trying to time align the low and high frequencies, so the best and most consistent way to do this is to use more small wires that add up to the low frequency DCR needs, and are small enough to force the wire to see more and more cross sectional current usage at higher frequencies. This means several small insulated wires that all need to be the same “single” wire.

The unique woven design does a lot to reduce inductance and associated capacitance. How is 59% reduced inductance over a single bonded pair achieved?

a. Electromagnetic field cancellation

Bonded-pair like polarity wires. Allows star quads to be formed throughout the weave

Separate polarity fields are not parallel, to reduce field reinforcements. Fields between polarities have some cancellation since they cross at angles, and are not ever parallel. (Wires that cross at ninety degrees cancel completely)

b. Capacitive reduction

Woven pattern averages out the wire-to-wire distances significantly. Woven pattern separates the wires, and “tricks” the bulk capacitive value to be far lower

The last point on the capacitive reduction is also what we like in a flat design, but it is inconsistent. Average distance between any two wires in a braided polarity, and thus between polarities, is far more consistent. The weave moves all the wires evenly, and consistently, to a closest proximity position and a maximum proximity position throughout the weave. Capacitance and inductance do vary, but in a controlled and expected way. The fattened weave holds overall capacitance to an unexpectedly low value of 45 pF/foot in a cable with such high conductor count.

Low inductance leverages the same current direction in the bonded pairs, combined with the star-quad wire geometry periodicity. And finally, the tight textile weave between polarity halves, forces a low loop area, and with wires never being parallel, further reducing inductance.

The overall reactance of the cable is shown in the graph below:

The chart illustrates a significant drop (yellow trace) in cable impedance compared to 1313A (blue trace). We know why this happened. The velocity, although variable, is nearly the same at each specific swept frequency point. We need to look at frequency-by-frequency calculations. The capacitance is linear across the entire audio band so that’s a set value.

We have a set value of capacitance, and a nearly set value of velocity (there will be slight variation) at a given frequency. What is changing is fundamentally the capacitance between cable designs for “impedance” characterization. The impedance equation is influenced by the change in capacitance, and thereby is the lower measured impedance, as the capacitance is in the denominator of the impedance equation. Increasing the capacitance from ~16 pF/foot to ~45 pF/foot decreases ICONOCLAST cable impedance. Speaker cables require low inductance, and need to get there without shooting capacitance through the roof.

Design is the overriding requirement, and materials, alongside unprovable theory, are second. Now we know why ICONOCLAST has the capacitance it does, as I can balance the inductance to industry-leading values, and still keep capacitance low, yet not so low as to increase impedance too much relative to the input requirement. Cables go up in impedance as you drop in frequency, the opposite of what we want. Listening tests have to decide if the superb inductance or impedance matching with much higher cable capacitance is ideal. Quick calculations will show capacitance problems with 8 ohm cables at audio once an amplifier is attached.

Don’t ignore the reactive time constants of L and C. We want an 8 ohm cable with no L and C, and zero resistance, and you can’t do that. Getting cable “impedance” reasonably low is more reliably safe for amplifiers.

4) Shield material and design considerations

I kept this topic here on purpose. Some may already know that the signal levels of low impedance cables negate the need for a shield. And that’s a good thing because a shield over a speaker cable is darn near always a bad thing for two reasons:

A shield will always increase capacitance of the cable. The question is how much.

To mitigate the capacitance increase, the shield must be moved significantly away from the core polarities, increasing the size of the cable.

Shields are only beneficial if the environment demands them. View a shield as a rain coat; great if you have water flying around but a major hindrance if you don’t. Coaxial cables are an exception as the shield defines the cable’s natural impedance. The ground-plane proximity and uniformity are vitally important with short-wavelength RF cables. Coaxial cables allow just that. Audio is not RF, and these shields are more FUD devices (Fear, Uncertainty, and Doubt) than than actually beneficial. This is especially in speaker cables whose signals are orders of magnitude over the background noise.

Audio seldom needs shielding on low-impedance cables and this is because magnetic fields decay rapidly with distance. The best defense is to move the low-frequency electromagnetic cables away from one another. The foil and even braid shields are higher frequency shields that are ineffective at much below 1 MHz. Magnetic fields lines need low permeability shield material (something a magnet will stick to) to route flux lines away from sensitive devices. A Faraday cage is a good example of a magnetic shield device. Low permeability metallic shields are a pain to use because they are stiff and heavy. Distance is the best remedy.

5) Jacket design and material considerations

All ICONOCLAST cables use FEP (fluorinated ethylene propylene) as the jacket to reduce UV-sensitivity and plasticizer migration, and provide chemical resistance. The cables are designed to last decades.

Summary

Little has been left to chance in the design of ICONOCLAST cables. All the products are born from strict measurements and the management of known electrical parameters. Belden’s philosophy is to make as low and R, L, and C cables as technically capable. The improvement to some may be unimportant. To others, and using different systems, they can be significant. The closer we manage the knowns, the better the tertiary elements will move along with those improvements.

All cables “react” differently. ICONOCLAST is designed to offer the most benign interaction possible between your amplifier and speaker by leveraging high-speed digital design principles to the much more complex audio band.

Galen is 100% reliable. Belden, at least in their “attempt” at marketing and selling retail, not so much. It blows my mind that a company with one of the best lines in this category can’t move this into the market. This is not the first time Galen has engineered unique, best in class designs for Belden (not audio) that have been successful (understatement). The weak link here is the company’s interface with the public where they appear incompetent. I’ve stated my biases before and have not compared them to every cable on the market but they best some of the most prominent and *vastly more expensive* offerings available. In particular this applies to the newest 4X4 interconnects. Without mentioning names, he has received complements from other manufacturers at shows and one story involved a switch (customer’s request) that occurred in a room where a competitor rep though they were his own speaker cables and proceeded to gush about how good they suddenly were. Maybe you were in the room at Axpona when this happened, it caused quite the stir. Another former rep for an exceedingly expensive line of cables ($67K speaker pair) sold his and purchased Belden Iconoclast.
Anyone want to take these over and market them? It’s beyond my pay grade, I’m just a nerd who loves audio.

Galen did email me promptly with info and a price list. They are out of my price range but, as you say less than their high end competition. I hope in the future a lower cost version may be available as I would really love to try them. The work and research that went into making them is impressive.

I’ve gotten several questions on how a cable can have the “same” exact velocity of propagation yet sound so different. That’s a very good question.
Where it is possible, ICONOCLAST uses AIR nearest the conductor to mitigate the signal slew rate, or the rate at which a signal can become an electromagnetic field. The reactive nature of the dielectric CLOSEST to the wire impacts how the signal’s shape is created, but NOT the speed down the wire.
The speed of the electromagnetic field down the wire at each frequency, it changes at every frequency through the audio band, is a superposition of all the materials between the wire and the ground plane. In a RCA shielded cable, this is from the conductor surface to the inner surface of the metal braid. It is between the two polarity wires in an XLR cable that also capacitive couple to the outer shield. If the outer shield is removed, the capacitance of an XLR drops.
In ICONOCLAST, we measure 87% VP at. Why not 100%? Because the electromagnetic signal sees ALL the materials, air, FEP spacer thread, and then the FEP tube in the case of the RCA, or the FEP filler in the XLR. This averages LOWER than AIR.

A cable can use solid plastic, foamed plastic, or air and then solid plastic (wire suspended inside a tube). In each case the “average” dielectric constant; (VP= 1/ SQRT(e) (e=dielectric constant) could be designed the same, but the signal RISE TIME won’t be as this responds to L and C variables. The speed of the signals down the wire will still be 87% at RF and ~50% to 5% in the audio band. The SHAPE of the voltage waveform will be different based on the slew rates of the dielectric mediums. The curve shape from min to max is reactively altered. Technically a cable looks like a system with multiple rise times between the ground references. Step dielectric rise times are not linear in time based measurements. Rise “time” equations (BW = 0.35/RT) define the 10-90% amplitude time. Our ears listen to ALL the voltage slope change from 0%-100% not just a time period number from 10-90%. Reactance alters the voltage change but not the speed the waveform moves down the wire once the electromagnetic field is created.
Speaker cables can effectively use SOLID dielectric as the AIR around the wire is very near the surface of an 8-mil FEP dielectric on the wire in ICONOCLAST. The signal is VERY robust and magnetically extends well outside of the dielectric so it is in “air” a good part of the time. How do we know this? Solid FEP has a speed of 69% at RF, but we measure 75% as the field is partly in air. This isn’t the case with interconnects that have smaller electromagnetic fields trapped inside a conductive shield.
Knowing the signal strength (magnetic field’s reach) determines the trade-offs to using air verses solid dielectric materials.

You guys are TOUGH!
OK, why would the air be best nearest the wire I’ve been asked? If you look at a sinewave, the signal amplitude change is most aggressive at the amplitude CHANGE from zero (up or down in voltage). This equates to the need for a faster response to mitigate distortion of the sinewave nearest the zero voltage point. A square wave is many, many sinewaves with the most distortion being from improperly constructed higher frequency sine waves (upper edge roll-off). Slew rate limiting of the leading edge of a sinewave is apparently more audible than when it is near maximum amplitude, making the faster rise time work best nearest the wire (from the origin of the electromagnetic wave).
Trial by ear conclusively says AIR near the wire had by far the largest positive impact on the sound field. We don’t have fixed dielectric (wire, spacer rod, and plastic then braid in an RCA, even more complex in an XLR).
The electromagnetic wave travels at average VP of all of the layers AFTER it “knows” what they all are when it hits the inside of the shield. But the SHAPE of the signal CHANGES as it transitions through each dielectric layer.
Capacitance and reactance are is also variable and defined by each dielectric layer, even though I report a “bulk” number for the cable.

My knowledge base stops right about here, but if we have some material science experts…let us know more.

Hi Galen, I have a couple of questions. You say that speaker wires have 20-30 amps running through them, what is the voltage?
I am not knowledgeable about wire, other than understanding gauge and basic home wiring. I took a basic course in industrial electricity, about 40 years ago. So, I don’t possess any real knowledge. So I may not have [more like didn’t] understood everything you have shared.
My second question is, if I understood correctly, most of the signal travels on the outer surface of a wire, that being the skin effect? Ok, what is the reason or benefit of using silver plated copper wire? I thought I understood the benefit of using solid silver wire, that it was a better conductor than copper, but since I have read all of your articles here, I am not sure of any of my past knowledge.
That might actually be three or four questions. I want you to know that I appreciate the time you have taken to explain the complexity of audio cables, thank you.

Hi jjeffstarr,
The voltage is low in speaker cables, 50 volts or so. Like CPU’s low voltage but lots of current.

The “signal” is an electromagnetic field between the dielectric and the ground reference. The electromagnetic field isn’t “in the wire” it is around the wire. What is IN the wire is the ELECTRON flow. This electron flow is distributed based on the frequency of the signal through the wire based on skin effect. When voltage, a potential, is turned into a current flow based on a wire’s resistance, it creates the electromagnetic field around the wire.

Silver is a better CONDUCTOR (attenuation properties) but it isn’t as nearly COHERENT as copper based on the SKIN depth with copper reaching more uniform current through the wire at a larger wire size than silver. Audio cables are short, so classic attenuation isn’t the issue, but signal time and phase alignment are more problematic. Getting cable’s frequency delivery in phase and in time is more audible than simple attenuation. Copper gets the job done easier than silver as it has a deeper skin depth. I can send you an analysis if you like. Sorry, it is pure physics of how the materials work so no magic. A really curious conclusion is reached based on material science. Gold, Silver and Copper all lose out to this one material. What is it?

Silver on the SURFACE of a wire improves the solder processing. It improves surface resistivity as silver oxide is a better conductor than copper oxide. The primary fundamental signals of music are well below the skin depth of the 40 micro inch thickness of the silver layer in ICONOCLAST, thus the high frequency harmonics are all that is changed using silver…and only if they are in the recordings. I urge people to listen to both the ETPC and the SPETPC as a direct comparison. Same R, L and C using either copper design. The Silver layer is too thin to offer meaningfully lower resistance so no bragging rights there.